1. Field of the Invention
This invention relates to lawn trimmers equipped with a flexible line cutting edge and more particularly, to bobbin housings for such lawn trimmers.
2. Description of the Prior Art
Lawn trimmers are devices which cut grass, weeds, etc. by using an engine or motor to drive rotary cutting edges. The rotary cutting edges are usually metal blades which can create hazards depending on the conditions of use and which are also undesirable in that damage is done either to trees or to the rotary cutting edges whenever the machine is used to trim under growth, grass, etc. around trees or in the vicinity of walls or other structures.
Accordingly, lawn trimmers which utilize the whirling motion of soft pliable flexible nylon cord have been developed and have to some extent been put to practical use. However, various drawbacks have been encountered in the handling and operation of such devices. In particular, due to structural defects in the bobbin used for the storage and extension of the nylon cord which is employed as the flexible line, and to defects in the bobbin housing, it is difficult to rewind an overextended cord. Furthermore, the extension of the cord often becomes impossible due to the twisting of two lengths of nylon cord inside the single bobbin. In addition, the cord is easily cut due to the fact that it is extended from the circumference of the housing. Also, the machine is easily fouled by the penetration of refuge material into the interior of the housing.
The simplest conventional lawn trimmer is equipped with flexible line cutting edges (such as disclosed in U.S. Pat. No. 3,826,068 and 3,859,776) are designed as shown in FIG. 1. FIG. 1 is a cross sectional representation of such a prior art device. In FIG. 1, the bobbin housing 1 is rigidly mounted on a rotary shaft 2 and is shaped in the form of a cover with an open bottom. The bobbin 3 is inserted in the housing from below and is clamped in place from beneath by a clamping plate 4. Projection 6 on the bobbin fit into holes 5 in the top of housing 1 so that the bobbin and housing rotate as a single unit. In this design, the flexible line 7 can be extended by loosening the clamping plate 4 so that the projections 6 are removed from the holes 5. However, the line cannot be rewound on the bobbin in this condition. To do this, it is necessary to remove the bobbin from the housing. Since the line cannot easily be rewound, it is not possible to easily shorten the length of the extended flexible line. Accordingly, it is difficult to adjust the length of the line to suit the type and condition of the growth of weeds, etc. that ought to be trimmed. Furthermore, since the flexible line 7 projects directly outward from the side wall of the housing 1, accidental contact between the perimeter of the housing 1 and a concrete wall, etc. leads to the immediate cutting of the flexible line, an undesirable result.